Monthly Archives: September 2010

After appearing to reach its annual minimum extent on September 10, and beginning to freeze up, Arctic sea ice again declined for several days. Ice extent reached its lowest value for the season on September 19, 2010, and has now been expanding for seven days.

Figure 1. Daily Arctic sea ice extent on September 19, 2010 was 4.60 million square kilometers (1.78 million square miles). The orange line shows the 1979 to 2000 median extent for that day. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data. —Credit: National Snow and Ice Data CenterHigh-resolution image

Overview of conditions

After appearing to reach a low point on September 10, sea ice extent rose for three days and then began a second decline. Ice extent dropped to its lowest extent for the year on September 19, at 4.60 million square kilometers (1.78 million square miles) .

Figure 2. The graph above shows daily Arctic sea ice extent as of September 26, 2010, along with daily ice extents for years wtih the previous four lowest minimum extents. The solid light blue line indicates 2010; orange shows 2009, pink shows 2008; dashed green shows 2007; light green shows 2005; and solid gray indicates average extent from 1979 to 2000. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data. —Credit: National Snow and Ice Data CenterHigh-resolution image

Conditions in context

The revised minimum ice extent on September 19 occurred ten days later than the average date of the minimum ice extent for the period 1979 to 2000, and 8 days later than the 1979 to 2009 average. With the additional days of ice loss, 2010 is no longer the shortest period of summer ice loss since 1979.

Figure 3. This image compares differences in ice-covered areas between September 19, 2010, the date of this year’s minimum, and September 16, 2007, the record low minimum extent. Light gray shading indicates the region where ice occurred in both 2007 and 2010, while white and dark gray areas show ice cover unique to 2010 and to 2007, respectively. Sea Ice Index data. —Credit: National Snow and Ice Data CenterHigh-resolution image

2010 minimum ice extent compared to 2007

Compared to the 2007 seasonal minimum, the 2010 minimum had less ice in the northern Beaufort Sea region, the East Greenland Sea and the western Laptev Sea. However, there was much more ice in the East Siberian Sea this year compared to 2007.

Final analysis pending

In the beginning of October, NSIDC will issue a formal announcement with a full analysis of the melt season, and graphics comparing this year to the long-term record. We will also announce the monthly average September sea ice extent, the measure scientists rely on for accurate analysis and comparison over the long term.

We will continue to post analyses of sea ice conditions throughout the year, with frequency determined by sea ice conditions. The near-real-time daily image update will continue each day.

For previous analyses, please see the drop-down menu under Archives in the right navigation at the top of this page.

Although ice extent appeared to reach a minimum on September 10, rising afterwards for three straight days, it has subsequently declined even further. NSIDC scientists are closely monitoring the ice extent and will provide another update on the data, as conditions develop.

Our season-end announcement in October will provide the final numbers for the minimum extent, as well as the monthly data for September, which scientists use for establishing long-term trends.

Arctic sea ice appears to have reached its annual minimum extent on 10 September. The minimum ice extent was the third-lowest in the satellite record, after 2007 and 2008, and continues the trend of decreasing summer sea ice.

Figure 1. Daily Arctic sea ice extent on September 10, 2010 was 4.76 million square kilometers (1.84 million square miles). The orange line shows the 1979 to 2000 median extent for that day. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data. —Credit: National Snow and Ice Data CenterHigh-resolution image

Overview of conditions

On September 10, 2010 sea ice extent dropped to 4.76 million square kilometers (1.84 million square miles). This appears to have been the lowest extent of the year; sea ice has now begun its annual cycle of growth.

Figure 2. The graph above shows daily Arctic sea ice extent as of September 13, 2010, along with daily ice extents for years wtih the previous four lowest minimum extents. The solid light blue line indicates 2010; orange shows 2009, pink shows 2008; dashed green shows 2007; light green shows 2005; and solid gray indicates average extent from 1979 to 2000. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.

This is only the third time in the satellite record that ice extent has fallen below 5 million square kilometers (1.93 million square miles), and all those occurrences have been within the past four years. The minimum for 2009 was 5.10 million square kilometers (1.97 million square miles), fourth lowest in the satellite record.

Despite a late start to the melt season, the ice extent declined rapidly thereafter, with record daily average ice loss rates for the Arctic as a whole for May and June. Assuming that we have indeed reached the seasonal minimum extent, 2010 would have the shortest melt season in the satellite record, spanning 163 days between the seasonal maximum and minimum ice extents.

Figure 3. This image compares differences in ice-covered areas between September 10, 2010, the date of this year’s minimum, and September 16, 2007, the record low minimum extent. Light gray shading indicates the region where ice occurred in both 2007 and 2010, while white and dark gray areas show ice cover unique to 2010 and to 2007, respectively. Sea Ice Index data. About the data. —Credit: National Snow and Ice Data Center High-resolution image

Comparison of the 2010 and 2007 September minima

At the 2010 seasonal minimum, ice remained fairly extensive in the East Siberian Sea, compared to 2007, when this area was ice free. 2010 ended up having less ice than 2007 in the Beaufort Sea and in the East Greenland Sea. Both the Northwest Passage and Northern Sea Route (along the shores of Eurasia) were open at the 2010 sea ice minimum, whereas in 2007, ice blocked part of the Northern Sea Route.

Figure 4. This image, from the NASA MODIS sensor on the Aqua satellite on September 14, shows new ice (dark gray region within circled area) is evident, growing outward from the remaining ice pack (white colored region) in the northwestern East Siberian Sea. The new ice appeared within the previous two days. —Credit: NSIDC courtesy NASA/GSFC MODIS Rapid ResponseHigh-resolution image

Evidence of freeze onset

Visible imagery from the NASA Moderate Resolution Imaging Spectroradiometer (MODIS) confirms that freeze-up is starting in some parts of the Arctic. Growth of new ice is visible in the image from September 14, 2010 extending off the remaining ice pack in the northwestern part of the East Siberian Sea. The new ice formed within the past couple days. Extent may still be declining in other regions, primarily due to heat from ocean waters.

A word of caution on calling the minimum

Because of the variability of sea ice at this time of year, the National Snow and Ice Data Center determines the minimum using a five-day running mean value. We have now seen four days of gains in extent. It is still possible that ice extent could fall slightly, because of either further melting or a contraction in the area of the pack due to the motion of the ice. For example, in 2005, the time series began to level out in early September, prompting speculation that we had reached the minimum. However, the sea ice contracted later in the season, again reducing sea ice extent and causing a further drop in the absolute minimum. When all the data for September are in, we will confirm the minimum ice extent for the season.

Final analysis pending

In the beginning of October, NSIDC will issue a formal announcement with a full analysis of the melt season, and graphics comparing this year to the long-term record. We will also announce the monthly average September sea ice extent, the measure scientists rely on for accurate analysis and comparison over the long term.

We will continue to post analyses of sea ice conditions throughout the year, with frequency determined by sea ice conditions. The near-real-time daily image update will continue each day.

For previous analyses, please see the drop-down menu under Archives in the right navigation at the top of this page.

Arctic sea ice generally reaches its annual minimumextent in mid-September. This August, ice extent was the second lowest in the satellite record, after 2007. On September 3, ice extent dropped below the seasonal minimum for 2009 to become the third lowest in the satellite record.

The Northwest Passage and the Northern Sea Route are largely free of ice, allowing the potential for a circumnavigation of the Arctic Ocean. At least two expeditions are attempting this feat, the Norwegian explorer Borge Ousland and the Peter I yacht from Russia.

Figure 1. Arctic sea ice extent for August 2010 was 5.98 million square kilometers (2.31 million square miles). The magenta line shows the 1979 to 2000 median extent for that month. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data. —Credit: National Snow and Ice Data CenterHigh-resolution image

Overview of conditions

Average ice extent for August was 5.98 million square kilometers (2.31 million square miles), 1.69 million square kilometers (653,000 square miles) below the 1979 to 2000 average, but 620,000 square kilometers (240,000 square miles) above the average for August 2007, the lowest August in the satellite record. Ice extent remained below the 1979 to 2000 average everywhere except in the East Greenland Sea near Svalbard.

The minimum ice extent for the year will probably occur in the next two weeks. NSIDC scientists are closely monitoring conditions and will report the minimum when it occurs.

Figure 2. The graph above shows daily Arctic sea ice extent as of September 6, 2010, along with daily ice extents for years wtih the four lowest minimum extents. The solid light blue line indicates 2010; orange shows 2009, pink shows 2008; dashed green shows 2007; light green shows 2005; and solid gray indicates average extent from 1979 to 2000. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.—Credit: National Snow and Ice Data CenterHigh-resolution image

Conditions in context

At the end of August, ice extent had fallen to the fourth lowest in the satellite record, behind the seasonal minima recorded for 2007, 2008, and 2009. On September 3, ice extent fell below the seasonal minimum for 2009 to claim third lowest on record, with perhaps one to two weeks left in the melt season.

The daily rate of decline for August was 55,000 square kilometers (21,000 square miles) per day, close to the 1979 to 2000 average of 54,000 square kilometers (21,000 square miles).

Figure 3. Monthly August ice extent for 1979 to 2010 shows a decline of 8.9% per decade. —Credit: National Snow and Ice Data Center High-resolution image

August 2010 compared to past years

Ice extent for August 2010 was the second lowest in the satellite record for the month. The linear rate of decline of August ice extent over the period 1979 to 2010 is now 8.9% per decade.

Figure 4. This map of sea level pressure for August 2010 shows a return of the dipole anomaly, which was present in June but not in July.—Credit: NSIDC courtesy NOAA/ESRL PSDHigh-resolution image

Return of the dipole anomaly

In August, a pattern of higher than average pressure over the northern Beaufort Sea and lower than average pressure over the Siberian side of the Arctic replaced the stormy and cool weather conditions that persisted through July. This atmospheric pattern, known as the dipole anomaly, brought relatively warm southerly winds into the Beaufort and Chukchi seas, where air temperatures were 1 to 3 degrees Celsius (1.8 to 5.4 degrees Fahrenheit) above normal for the month of August. The warmth enhanced melt in the region, and southerly winds contributed to ice loss by pushing the ice edge northward. This pattern is similar to the pattern at the end of the 2007 melt season, but not as pronounced. Air temperatures this August were also 1 to 3 degrees Celsius (1.8 to 5.4 degrees Fahrenheit) below normal over the Barents and Kara Seas.

Figure 5. This image from NASA’s MODIS sensor on the Aqua satellite on August 25, 2010, shows open water and low-concentration ice in the Beaufort Sea, the region where large amounts of rotten ice were observed last year.—Credit: National Snow and Ice Data Center courtesy NASA/GSFC MODIS Rapid ResponseHigh-resolution image

Rotten ice in the Beaufort and Chukchi seas

Last year, Dave Barber, a researcher from the University of Manitoba, reported unusual conditions in the Beaufort Sea with large regions of rotten ice. Satellite imagery from the NASA Moderate Resolution Imaging Spectroradiometer (MODIS) and Advanced Microwave Scanning Radiometer – Earth Observing System (AMSR-E) sensors suggest similar conditions this year in the Beaufort and Chukchi seas, where there are large areas with unconsolidated ice floes and low ice concentration.

Figure 6. This graph of regional ice loss in the Arctic shows faster than normal ice loss in the Beaufort and Chukchi seas, and slower than normal ice loss in the East Siberian Sea and Central Arctic. The map in the bottom left corresponds to the regions plotted across the top of the graph. Colors in the bar graph correspond to August ice loss in different years.—Credit: National Snow and Ice Data Center High-resolution image

Regional ice loss

The rate of ice loss in the summer varies from region to region depending on local air and ocean temperatures and wind patterns. This August, the decline in ice extent was unusually fast in the Beaufort and Chukchi Sea, likely because of the rotten ice that melted out completely. In addition, southerly winds linked to the dipole anomaly pattern brought warmer air into the region and helped push the ice edge northward.

However, the loss rate in the East Siberian Sea and the Central Arctic was slower than any of the past three years, and was also fairly slow (slower than the 1979 to 2000 average rate) in the Laptev and Kara Seas. The reason for slow ice loss in the Kara Sea, however, is that there was already very little ice in that region at the beginning of August. Such year-to-year variations demonstrate the importance of weather conditions in determining regional ice loss.